TMD-based Structural Vibration Control Of Offshore Wind Turbines And Investigation Of A New Semi-submersible Floating Foundation

With increasing concerns about environmental pollution and soaring fuel prices,the world’s interest in renewable energy is growing.Wind energy is the most attractive and environmentally friendly energy source for large-scale power generation,but it requires the development of large-scale wind farms.In metropolitan areas with high demand for electricity,onshore wind energy resources are limited,and land for large-scale wind farms is scarce.However,most metropolises in the world are located in coastal areas.Wind energy has obvious advantages,that is,it does not require land use and wind energy is more stable.There are huge wind resources in the deep seas near coastal cities in China.At present,fixed-bottom offshore wind turbines of monopiles are commercially available.However,the research on the dynamic response and structure control of the wind turbine is not comprehensive enough,and the wind turbine structure vibration control under the combined action of wind and wave loads in different directions is rarely considered.At the same time,tuned mass dampers（TMD）are mostly used for structural control of wind turbines,and almost all TMDs are installed in the nacelle,with relatively small volume and mass,and very limited results.Therefore,there is an urgent need to develop a structural control system for offshore wind turbines and a floating foundation platform that adapts to complex wind and wave environmental conditions,so that offshore energy sources are reliable and economically feasible.This paper firstly carries out the structural dynamic response analysis of the offshore monopile wind turbine under the situation of wind wave misalignment,and develops an omnidirectional tuned mass damper system for structural vibration control.Then,several semi-submersible platform foundations were improved and tested.Finally,the vibration control of the deep-sea semi-submersible wind turbine is carried out by establishing a model of the omnidirectional TMD system installed on the top of the wind turbine and the platform,and then considering the structural control under the combined action of wind and waves,especially for the situation of wind wave misalignment.Explore the effect of passive structure control technology applied to offshore wind turbines and verify the scientific rationality of the platform foundation developed.The research results show that the omnidirectional TMD system developed for offshore monopile wind turbines can achieve very good results in structural vibration control.The addition of the TMD system will have an almost uniform positive impact on the overall wind turbine system,significantly reducing the fore-aft and side-to-side loads of the tower.It is proved that the omnidirectional TMD system is a relatively cheap and robust solution to suppress the vibration of the tower in the offshore environment to reduce the fatigue load.Based on the semi-submersible platform prototype,a new type of semi-submersible platform with different numbers of offset columns but the same total weight is proposed.By increasing the number of offset columns,the dynamic performance of surge,heave and pitch motions can be improved.Especially for the surge motion.Considering the misalignment of wind and wave loads,the effectiveness of the TMD system for damping the floating wind turbine was verified,and the excellent effect of installing the TMD system in the nacelle and platform at the same time was further tested and verified.